1. Field of the Invention
This invention relates to a technical field of a pre-pit detecting device for detecting pre-pits as pre-information formed on a high density recording medium such as DVD-R (DVD-Recordable) or DVD-RW (DVD-Rerecordable). Especially, the invention relates to a technical field of a pre-pit detecting device capable of setting a binarizing level for generating pre-pit signals to an optimum one.
2. Description of Prior Art
Generally, on a recordable optical recording medium (disc), or a reference signal to generate address information and a clock signal for a use of recording and reproducing operation is recorded in advance in form of pre-pits or pre-groove on the optical record information in which record information is not recorded yet. For example, on DVD-R (Digital Versatile Disc-Recordable), a pre-groove, which is an area where information to be originally recorded such as video data or audio data is recorded as recording pits, and pre-pits (hereinafter referred to LPP (Land pre-pit)) on a land portion, which is an area between the pre-grooves, are recorded.
The pre-groove is slightly wobbled in the radius direction of the disc with a frequency (hereinafter referred to wobbling frequency) based on a reference clock used for rotate control of DVD-R. In the rotate control, the wobbling frequency is detected, and a feedback control is performed so that the wobbling frequency matches the frequency of the reference clock.
The LPPs are detected as follows: First, reflected light of a light beam applied to the pre-groove is received in a photo receiving unit, which is divided in two by a parting line at least optically parallel to the direction of a tangent to the pre-groove. Then, a difference signal (hereinafter referred to radial push-pull signal) is generated by computing a difference between a first readout signal and a second readout signal generated on the basis of electrical signals outputted from the photo receiving unit. The radial push-pull signal is compared with a predetermined binarizing level by an LPP signal binarizing circuit, so that a binarized signal (hereinafter referred to LPP signal) is generated. In accordance with the LPP signal detected by the above-mentioned processes, address information indicating the position of recording/reproducing on the recording medium, a recording clock signal for a use of recording operation and the like are generated.
The radial push-pull signal is a composite signal where the LPP is piggybacked onto the wobbling frequency components because of wobbling of the pre-groove in the direction of a radius of the disc as described above.
However, in a disc where information is recorded in high density such as DVD-R, there is a case where crosstalk between wobbling signal components of a pre-groove and those of adjacent pre-groove to which a light beam applies is occurred.
In the case where the crosstalk is occurred, interference between the wobbling signal components in the composite signal obtained as the radial push-pull signal and those of the adjacent pre-groove, is occurred, so that the amplitude of the wobbling signal is changed.
Therefore, the LPP signal components are piggybacked onto the wobbling signal, and the amplitude of the wobbling signal which becomes a base line voltage is changed, so that it is difficult to compare the radial push-pull signal with a fixed binarizing level in order to detect the LPP signal as a binarized signal.
An optimum value of a slice level such as the binarizing level differs according to uses of the LPP signal, for example, the generation of the address information or the generation of the recording clock signal. For the generation of the recording clock signal, it is enough to obtain a cycle of the LPP, so that it is unnecessary to detect the whole of the LPPs piggybaked onto the wobbling signal. However, binarizing noise components to obtain pseudo-LPP signal adversely affects the detection of the cycle, so that it is preferable that the binarizing level is as high as possible to make noise components reduce.
For the generation of the address information, if there are pseudo-LPP signals due to noise components more or less, it is preferable that the LPP signals piggybacked onto the wobbling signal are reliably detected. If proper LPP signals are reliably detected, it is possible to find and eliminate the pseudo-LPP signals. Therefore, it is preferable that the binarizing level is as low as possible in order to reliably detect the LPP signals.
The invention has been made in view of the above problems addressed by the prior art. An object of the invention is, therefore, to provide a pre-pit detecting device and a binarizing level setting method capable of immediately setting the binarizing level for a use of binarizing the LPP to optimum value.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal; and a first gate for periodically opening its gate only in a period during which the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate, wherein the binarizing level setting device counts the number of the pre-pit signals passing through the first gate and sets the binarizing level based on the relationship between the counted number per a reference time and a predetermined reference number.
According to the present invention, a composite signal in which pre-pit signal components are superimposed onto frequency components of wobbling, is extracted from an optical recording medium. The composite signal is binarized, so that pre-pit signals are generated. The pre-pit signals pass through a first gate when the gate is open. The gate is periodically opened only in a period during which the amplitude of the wobbling becomes a maximum one. The number of the pre-pit signals passing through the gate is counted, so that a binarizing level for generating the pre-pit signal is set based on the relationship between the counted number per a reference time and a predetermined reference number. Accordingly, since it is possible to grasp whether the binarizing level is set to a higher one or lower one, it is possible to set the binarizing level to an optimum one immediately.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal, components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal; and a second gate for periodically opening its gate only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate, wherein the binarizing level setting device counts the number of the pre-pit signals passing through the second gate and sets the binarizing level based on the relationship between the counted number per a reference time and a predetermined reference number.
According to the present invention, a composite signal in which pre-pit signal components are superimposed onto frequency components of wobbling, is extracted from an optical recording medium. The composite signal is binarized, so that pre-pit signals are generated. The pre-pit signals pass through a second gate when the gate is open. The gate is periodically opened only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one. The number of the pre-pit signals passing through the gate is counted, so that a binarizing level for generating the pre-pit signal is set based on the relationship between the counted number per a reference time and a predetermined reference number. Accordingly, it is possible to set the binarizing level to an optimum one immediately. In addition, since the second gate is opened only in a period during which the pre-pit signal components are invariably superimposed on the wobbling, it is possible to count the pre-pit signals precisely. Therefore, the binarizing level which is set based on the relationship between the above-mentioned counted number per the reference number and the predetermined reference number, can be set to a more optimum one.
In one aspect of the present invention, the binarizing level setting device compares the counted number per the reference time with the predetermined reference number, and sets the binarizing level based on the results of comparing.
According to this aspect, it is possible to set the binarizing level to an optimum one immediately based on the results of comparing.
In another aspect of the present invention, the binarizing level setting device raises the binarizing level in the case where the counted number per the reference time is larger than the predetermined reference number, and lowers the binarizing level in the case where the counted number per the reference time is smaller than the predetermined reference number.
According to this aspect, it is possible to set the binarizing level to an optimum one immediately based on the counted number.
In further aspect of the present invention, the binarizing level setting device compares the counted number per the reference time with a predetermined range including the predetermined reference number, and sets the binarizing level based on the results of comparing.
According to this aspect, it is possible to set the binarizing level to an optimum one immediately based on the results of comparing. In addition, it is possible to ensure some margins of safety for setting the binarizing level.
In further aspect of the present invention, the binarizing level setting device raises the binarizing level in the case where the counted number per the reference time is larger than the predetermined range, and lowers the binarizing level in the case where the counted number per the reference time is smaller than the predetermined range.
According to this aspect, it is possible to set the binarizing level to an optimum one immediately based on the counted number. In addition, it is possible to ensure some margins of safety for setting the binarizing level.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal; a first gate for periodically opening its gate only in a period during which the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate; and a second gate for periodically opening its gate only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate, wherein the binarizing level setting device counts the number of the pre-pit signals passing through the first gate and the second gate respectively, and sets the binarizing level based on both the relationship between the number of the pre-pit signals passing through the first gate per a reference time and a predetermined first reference number, and the relationship between the number of the pre-pit signals passing through the second gate per a reference time and a predetermined second reference number.
According to the present invention, a composite signal in which pre-pit signal components are superimposed onto frequency components of wobbling, is extracted from an optical recording medium. The composite signal is binarized, so that pre-pit signals are generated. The pre-pit signals pass through a first gate when the gate is open. The first gate is periodically opened only in a period during which the amplitude of the wobbling becomes a maximum one. Further, the pre-pit signals pass through a second gate when the gate is open. The second gate is periodically opened only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one. The number of the pre-pit signals passing through the first gate is counted, and the number of the pre-pit signals passing through the second gate is counted. Then, a binarizing level for generating the pre-pit signal is set based on the relationship between the number of the pre-pit signals passing through the first gate per the reference time and the predetermined first reference number, and the relationship between the number of the pre-pit signals passing through the second gate per the reference time and the predetermined second reference number. Accordingly, the binarizing level is set at two stages, it is possible to set the binarizing level to more optimum one.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal; and a first gate for periodically opening its gate only in a period during which the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate, wherein the binarizing level setting device gradually lowers the binarizing level from a high level to a low level, and counts the number of the pre-pit signals passing through the first gate during a reference time in each level and sets a level where the counted number per the reference time becomes within a predetermined range including the predetermined reference number as a reference binarizing level.
According to the present invention, while gradually lowering the binarizing level from a high level to a low level, the number of the pre-pit signals passing through the first gate is counted in each level during the reference time. Further, the level where the counted number per the reference time becomes within the predetermined range including the predetermined reference number, is set as the reference binarizing level. Therefore, since it is possible to grasp whether the binarizing level is set to a higher one or lower one, it is possible to set the binarizing level to an optimum one immediately. In addition, it is possible to set the reference binarizing level at an initial stage to an optimum one.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal; and a second gate for periodically opening its gate only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate, wherein the binarizing level setting device gradually lowers the binarizing level from a high level to a low level, and counts the number of the pre-pit signals passing through the second gate during a reference time in each level and sets a level where the counted number per the reference time becomes within a predetermined range including the predetermined reference number as a reference binarizing level.
According to the present invention, while gradually lowering the binarizing level from a high level to a low level, the number of the pre-pit signals passing through the second gate is counted in each level during the reference time. Further, the level where the counted number per the reference time becomes within the predetermined range including the predetermined reference number, is set as the reference binarizing level. Therefore, since the second gate is opened only in a period during which the pre-pit signal components are invariably superimposed on the wobbling, it is possible to count the pre-pit signals precisely. In addition, it is possible to set the reference binarizing level at an initial stage to an optimum one.
In one aspect of the present invention, the binarizing level setting device, after setting the reference binarizing level, raises the reference binarizing level in the case where the counted number per the reference time is larger than a predetermined range including the predetermined reference number, and lowers the reference binarizing level in the case where the counted number is smaller than the predetermined range.
According to this aspect, it is possible to set the reference binarizing level at an initial stage to an optimum one immediately.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the pre-pit signal for extracting at least address information as a binarizing level for an address, and for setting a binarizing level for the pre-pit signal for extracting at least a recording/reproducing clock as a binarizing level for a clock; a first pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level for an address to generate a pre-pit signal for an address; a second pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level for a clock to generate a pre-pit signal for a clock; and a first gate for periodically opening its gate only in a period during which the amplitude of the wobbling becomes a maximum one to make at least one pre-pit signal of the generated pre-pit signals pass through the gate, wherein the binarizing level setting devices gradually lower the respective binarizing levels from a high level to a low level, and count the number of the pre-pit signals passing through the first gate during a reference time in each level, and set a level where the counted number per the reference time becomes within a predetermined range including the predetermined reference number as a reference binarizing level, and sets the binarizing level for an address to a lower level than the reference binarizing level, and sets the binarizing level for a clock to a higher level than the reference binarizing level.
According to the present invention, Therefore, since it is possible to grasp whether the binarizing level is set to a higher one or lower one, it is possible to set the binarizing level to an optimum one immediately. In addition, it is possible to discriminate between the binarizing level for generating an pre-pit signal, which is used for generating the address information and various timing signals, and the binarizing level for generating another pre-pit signal, which is used for generating a recording clock signal, so that it is possible to set optimum binarizing levels for generating respective pre-pit signals.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the pre-pit signal for extracting at least address information as a binarizing level for an address, and for setting a binarizing level for the pre-pit signal for extracting at least a recording/reproducing clock as a binarizing level for a clock; a first pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level for an address to generate a pre-pit signal for an address; a second pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level for a clock to generate a pre-pit signal for a clock; and a second gate for periodically opening its gate only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate, wherein the binarizing level setting devices gradually lower the respective binarizing levels from a high level to a low level, and count the number of the pre-pit signals passing through the second gate during a reference time in each level, and set a level where the counted number per the reference time becomes within a predetermined range including the predetermined reference number as a reference binarizing level, and sets the binarizing level for an address to a lower level than the reference binarizing level, and sets the binarizing level for a clock to, a higher level than the reference binarizing level.
According to the present invention, Therefore, since the second gate is opened only in a period during which the pre-pit signal components are invariably superimposed on the wobbling, it is possible to count the pre-pit signals precisely. In addition, it is possible to discriminate between the binarizing level for generating an pre-pit signal, which is used for generating the address information and various timing signals, and the binarizing level for generating another pre-pit signal, which is used for generating a recording clock signal, so that it is possible to set optimum binarizing levels for generating respective pre-pit signals.
In one aspect of the present invention, the binarizing level setting device, after setting the binarizing levels, raises the reference binarizing level, the binarizing level for an address, and the binarizing level for a clock in the case where the counted number per the reference time is larger than the predetermined range including the predetermined reference number, and lowers the reference binarizing level, the binarizing level for an address, and the binarizing level for a clock in the case where the counted number is smaller than the predetermined range.
According to this aspect, based on the counted number, it is possible to discriminate between the binarizing level for generating an pre-pit signal, which is used for generating the address information and various timing signals, and the binarizing level for generating another pre-pit signal, which is used for generating a recording clock signal, so that it is possible to set optimum binarizing levels for generating respective pre-pit signals.
The above object of the present invention can be achieved by a binarizing level setting method of the present invention for setting a binarizing level for binarizing a composite signal extracted from an optical recording medium to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The binarizing level setting method is provided with the processes of: provisionally setting a binarizing level for the composite signal; comparing the extracted composite signal with the set binarizing level; generating a pre-pit signal based on the results of comparing; counting the number of the pre-pit signals passing through a first gate during a reference time, said first gate periodically opening its gate only in a period during which the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate; and setting the binarizing level based on the relationship between the counted number per the reference time and a predetermined reference number.
According to the present invention, since it is possible to grasp whether the binarizing level is set to a higher one or lower one, it is possible to set the binarizing level to an optimum one immediately.
The above object of the present invention can be achieved by a binarizing level setting method of the present invention for setting a binarizing level for binarizing a composite signal extracted from an optical recording medium to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The binarizing level setting method is provided with the processes of: provisionally setting a binarizing level for the composite signal; comparing the extracted composite signal with the set binarizing level; generating a pre-pit signal based on the results of comparing; counting the number of the pre-pit signals passing through a second gate during a reference time, said second gate periodically opening its gate only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate; and setting the binarizing level based on the relationship between the counted number per the reference time and a predetermined reference number.
According to the present invention, it is possible to set the binarizing level to an optimum one immediately. In addition, since the second gate is opened only in a period during which the pre-pit signal components are invariably superimposed on the wobbling, it is possible to count the pre-pit signals precisely. Therefore, the binarizing level which is set based on the relationship between the above-mentioned counted number per the reference number and the predetermined reference number, can be set to a more optimum one.
The above object of the present invention can be achieved by a binarizing level setting method of the present invention for setting a binarizing level for binarizing a composite signal extracted from an optical recording medium to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The binarizing level setting method is provided with the processes of: provisionally setting a binarizing level for the composite signal; comparing the extracted composite signal with the set binarizing level; generating a pre-pit signal based on the results of comparing; counting the number of the pre-pit signals passing through a first gate during a reference time, said first gate periodically opening its gate only in a period during which the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate; and counting the number of the pre-pit signals passing through a second gate during a reference time, said second gate periodically opening its gate only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate; and setting the binarizing level based on both the relationship between the number of the pre-pit signals passing through the first gate per the reference time and a predetermined first reference number, and the relationship between the number of the pre-pit signals passing through the second gate per the reference time and a predetermined second reference number.
According to the present invention, the binarizing level is set at two stages, it is possible to set the binarizing level to more optimum one.
The above object of the present invention can be achieved by a binarizing level setting method of the present invention for setting a binarizing level for binarizing a composite signal extracted from an optical recording medium to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The binarizing level setting method is provided with the processes of: provisionally setting a binarizing level for the composite signal; comparing the extracted composite signal with the set binarizing level; generating a pre-pit signal based on the results of comparing; counting the number of the pre-pit signals passing through a first gate during a reference time while gradually lowering the binarizing level from a high level to a low level, said first gate periodically opening its gate only in a period during which the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate; and setting a level where the counted number per the reference time becomes within a predetermined range including a predetermined reference number as a reference binarizing level.
According to the present invention, since it is possible to grasp whether the binarizing level is set to a higher one or lower one, it is possible to set the binarizing level to an optimum one immediately. In addition, it is possible to set the reference binarizing level at an initial stage to an optimum one.
The above object of the present invention can be achieved by a binarizing level setting method of the present invention for setting a binarizing level for binarizing a composite signal extracted from an optical recording medium to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The binarizing level setting method is provided with the processes of: provisionally setting a binarizing level for the composite signal; comparing the extracted composite signal with the set binarizing level; generating a pre-pit signal based on the results of comparing; counting the number of the pre-pit signals passing through a second gate during a reference time while gradually lowering the binarizing level from a high level to a low level, said second gate periodically opening its gate only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate; and setting a level where the counted number per the reference time becomes within a predetermined range including a predetermined reference number as a reference binarizing level.
According to the present invention, since the second gate is opened only in a period during which the pre-pit signal components are invariably superimposed on the wobbling, it is possible to count the pre-pit signals precisely. In addition, it is possible to set the reference binarizing level at an initial stage to an optimum one.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; and a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal, wherein the binarizing level setting device counts the number of the pre-pit signals generated by the pre-pit signal generating device and sets the binarizing level based on the relationship between the counted number per a reference time and a predetermined reference number.
According to the present invention, in the case where there is no pseudo- pre-pit signal or are few pseudo- pre-pit signal due to noise components, even if the above-mentioned gate is eliminated, it is possible to set the binarizing level to an optimum one immediately by counting the pre-pit signals and setting the binarizing level based on the relationship between the counted number per the reference time and the predetermined reference number.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; and a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal, wherein the binarizing level setting device gradually lowers the binarizing level from a high level to a low level, and counts the number of the pre-pit signals generated by the pre-pit signal generating device during a reference time in each level and sets a level where the counted number per the reference time becomes within a predetermined range including the predetermined reference number as a reference binarizing level.
According to the present invention, in the case where there is no pseudo- pre-pit signal or are few pseudo- pre-pit signal due to noise components, even if the above-mentioned gate is eliminated, it is possible to set the binarizing level to an optimum one immediately by counting the pre-pit signals and setting the binarizing level based on the relationship between the counted number per the reference time and the predetermined reference number.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the pre-pit signal for extracting at least address information as a binarizing level for an address, and for setting a binarizing level for the pre-pit signal for extracting at least a recording/reproducing clock as a binarizing level for a clock; a first pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level for an address to generate a pre-pit signal for an address; a second pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level for a clock to generate a pre-pit signal for a clock, wherein the binarizing level setting devices gradually lower the respective binarizing levels from a high level to a low level, and count the number of the pre-pit signals generated by the binarizing level setting device during a reference time in each level, and set a level where the counted number per the reference time becomes within a predetermined range including the predetermined reference number as a reference binarizing level, and sets the binarizing level for an address to a lower level than the reference binarizing level, and sets the binarizing level for a clock to a higher level than the reference binarizing level.
According to the present invention, in the case where there is no pseudo- pre-pit signal or are few pseudo- pre-pit signal due to noise components, even if the above-mentioned gate is eliminated, it is possible to set the binarizing level to an optimum one immediately by counting the pre-pit signals and setting the binarizing level based on the relationship between the counted number per the reference time and the predetermined reference number.
The above object of the present invention can be achieved by a binarizing level setting method of the present invention for setting a binarizing level for binarizing a composite signal extracted from an optical recording medium to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The binarizing level setting method is provided with the processes of: provisionally setting a binarizing level for the composite signal; comparing the extracted composite signal with the set binarizing level; generating a pre-pit signal based on the results of comparing; counting the number of the generated pre-pit signals during a reference time; and setting the binarizing level based on the relationship between the counted number per the reference time and a predetermined reference number.
According to the present invention, in the case where there is no pseudo- pre-pit signal or are few pseudo- pre-pit signal due to noise components, even if the above-mentioned gate is eliminated, it is possible to set the binarizing level to an optimum one immediately by counting the pre-pit signals and setting the binarizing level based on the relationship between the counted number per the reference time and the predetermined reference number.
The above object of the present invention can be achieved by a binarizing level setting method of the present invention for setting a binarizing level for binarizing a composite signal extracted from an optical recording medium to generate a pre-pit signal. The optical recording medium having an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The binarizing level setting method is provided with the processes of: provisionally setting a binarizing level for the composite signal; comparing the extracted composite signal with the set binarizing level; generating a pre-pit signal based on the results of comparing; counting the number of the generated pre-pit signals while gradually lowering the binarizing level from a high level to a low level; and setting a level where the counted number per the reference time becomes within a predetermined range including a predetermined reference number as a reference binarizing level,
According to the present invention, in the case where there is no pseudo- pre-pit signal or are few pseudo- pre-pit signal due to noise components, even if the above-mentioned gate is eliminated, it is possible to set the binarizing level to an optimum one immediately by counting the pre-pit signals and setting the binarizing level based on the relationship between the counted number per the reference time and the predetermined reference number.